Patent GB-768947-A (GB)
Title: Improvements in and relating to thermostatically controlled means for regulating the temperature of electric ovens and like cooking appliances
Inventor: WALTON GORDON HERBERT FRANCIS
IPC: H05B1/02
Filed: 1954-02-15
Abstract: 768,947. Automatic temperature control systems; control systems for heating resistors. DIAMOND H SWITCHES, Ltd. Feb. 8, 1955 [Feb. 15, 1954], No. 4338/54. Class 38(4). [Also in Group XXXVII] In a system for controlling the temperature of an electric oven, of the type in which separate " bake " and " grill " elements may both be switched on for preheating to a desired baking temperature, an electromagnet maintains the " grill " switch closed until thermostat contacts open at the desired temperature to de-energize the magnet and thus switch off the " grill element, the oven temperature being thereafter maintained by the " bake element only. The anti-clockwise movement of a manual control 6, Fig. 1, from the " off " position to a setting in the " baking range of oven temperatures results in the closing of thermostat contacts 1, 2, Figs. 1, 2, and the adjustment of the thermostat bellows 3, the " baking " element 13 being thus energized by A.C. from conductors 14, 16 over closed contacts 10, 12 until contacts 1, 2 re-open at the desired oven temperature. The clockwise setting of control 6 to the " grill " position results in the rotation of a disc-mounted cam 9 to cause a resilient contact-arm 10 to make with contact 11, the arm 10 being normally biased against contact 12, The " grilling element 17 is thus energized with A.C. until contacts 1, 2 re-open at the pre-set " grilling " temperature. If " preheating to a " baking temperature is required, element 17 is energized in addition to element 13 by pressing a button 25 to actuate a plunger 24. The latter is moved against the action of a spring 27 so that its conducting bridge member 19 makes resilient contacts 18, 20, thereby energizing element 17 and the winding 21 of an electromagnet 22. The plunger 24 also carries an armature 26 which makes with the shaded magnet poles 23 just after winding 21 is energized, the armature being thus attracted to maintain element 17 energized. When contacts 1, 2 re-open to de-energize winding 21, the plunger 24 is spring-urged to break contacts 18, 20 and de-energize element 17. Subsequent closing of contacts 1, 2 causes energizing of the " baking " element 13 only unless the button is pressed again. If the control 6 is moved to the " grill " position, the making of contact-arm 10 with contact 11 short-circuits the winding 21 to render the latter inoperative. In a modified circuit, Fig. 3, to prevent " over shoot " while preheating, additional thermostat contacts 29, 30 are arranged to open before contacts 1, 2, thereby de-energizing element 17 before the desired " baking " temperature is reached. A regulator, Fig. 8 (not shown), of the type described in Specification 517,538, [Group XXXVII], may be provided for manually-variable " on-off " control of the " grilling " element only, the circuit comprising essentially a bimetal contacting strip with an associated heater in series with the element. A neon is lit when the " baking " element is energized, and a combined switchindicator may replace the push-button for actuating plunger 24 to energize the " grilling " element.